Polymer blends which can be formed or shaped into lightweight and durable articles useful, for example, as automobile parts, toys, housings for various types of equipment, and the like are well known in the art. Unfortunately, with polymer blends derived from components such as polyethylene, polypropylene and rubber, it is difficult to paint articles formed therefrom so that the paint securely and durably adheres to the surface. The problem of paint adhesion is of particular concern in the case of articles made of blends derived from thermoplastic olefin ("TPO") compositions of the type disclosed, for example, in Kawai, U.S. Pat. No. 4,480,065 and Fukui et al., U.S. Pat. Nos. 4,412,016 and 4,439,573 which are expressly incorporated herein by reference thereto.
In particular, TPO compositions which are mechanical blends of synthetic rubber and polyolefins, such as polypropylene and polyethylene, are used for fabricating lightweight and durable products for use in the automotive industry and in various other applications. Because articles made from TPO compositions have gained acceptance in the automotive industry as substitutes for steel bumpers, body parts and the like, it is important to be able to paint such articles so that there is little visible difference between them and the metallic parts of the vehicle.
The utility of TPO blends would be expanded in automotive and other applications if the adhesion of paints to articles made from such blends were improved. Such other applications include flocked sheets for trunk liners and decorative rub strips which are currently being made of other plastics such as polyvinylchloride ("PVC") to which paints adhere better.
Unfortunately, articles made from polymer compositions containing substantial amounts of polyethylene (and/or polypropylene) and rubber are often difficult to paint so that the paint adheres permanently to them. In particular, most paints will either not initially adhere to the product or else peel or chip away under normal field use or high humidity conditions, or in the presence of fuels or solvents.
Various methods have been tried to make articles having substantial amounts of polypropylene and/or rubber therein more paint receptive. The use of primers or adhesion promoters as chlorinated polyolefins, and plasma surface treatment or other electronic surface treatments are examples. However, these prior methods for increasing the paint receptivity of such articles are costly and time consuming. The use of chlorinated polymers to promote adhesion between the surface of the article and the paint, as disclosed, for example, in the aforementioned U.S. Pat. No. 4,439,573, is required in state-of-the-art automotive applications; but even so, the gasoline and solvent resistance of painted TPO parts pretreated in this way has only been marginally acceptable.
It is therefore apparent that a need exists for polymer compositions that can be used to form paint receptive, durable and lightweight shaped articles which do not require surface pre-treatment.
Polymer blends derived from TPO have been used for film and packaging applications, as taught, for example, in Yoshimara et al., U.S. Pat. No. 4,454,303. Also, while prior compositions of polyolefins and copolymers of ethylene and ethylenically unsaturated carboxycic acids and ionomers have been used for improved ink adhesion and lacquer bonding, such compositions did not possess the physical properties needed for molding applications nor do they possess the high humidity resistance or high level of paint adhesion of the blends of the present invention. The present invention features the use of components which makes possible blends that are particularly suitable for injection molding. Such blends, when molded, exhibit remarkable and unexpected improvements in receptivity toward certain paints, including automotive paints, without sacrificing the other desirable properties of TPO blends.
PCT application PCT/US86/00315 discloses polymer blend formulations that can be formed to produce articles having paint receptive surfaces. The essential components of the blend are:
(A) a copolymer of ethylene and an ethylenically unsaturated carboxylic acid,
(B) an elastomer which is compatible with components (B) and (C) and
(C) a crystalline polypropylene homopolymer or crystalline polypropylene copolymer of ethylene wherein the ratio of the above components is such as to satisfy: EQU 0.18.ltoreq.B/(A+B).ltoreq.0.91
and EQU 0.43.ltoreq.C/(A+B).ltoreq.1.51
The paint receptive properties of articles made from the above polymer blends were tested for initial paint adhesion, resistance to solvents, resistance to humidity and resistance to delamination. Test data indicate high adhesion levels resulting in highly durable shaped articles.
U.S. patent application Ser. No. 07/387,407 similarly discloses thermoplastic compositions and articles made therefrom which have a high receptivity toward automotive paints comprising the components:
of a copolymer of an ethylenically unsaturated carboxylic acid and ethylene,
of an elastomer comprising an ethylene-alpha-olefin copolymer,
of a crystalline homopolymer or copolymer of propylene,
of polyethylene or a copolymer of ethylene and an alpha-olefin, and
optionally of an inorganic filler. The paint adhesion of the articles formed from these blends, however, are often unsatisfactory under high humidity conditions over a long period of time (i.e. 240 hours).
Accordingly, it is an object of the present invention to provide polymer blends that are useful for making lightweight, durable articles having paint receptive and adherent surfaces.
Another object of the invention is to provide lightweight and durable shaped articles made from polymer blends according to the invention and having paint receptive surfaces.
Another object is to provide durably painted shaped articles made from polymer blends according to the invention.
Another object is to provide methods for producing compositions in the form of polymer blends, shaped articles made from such blends having paint-receptive surfaces, and durably painted shaped articles.
Yet another object is to provide coating systems, coating additives and surface treatments suitable for use with the compositions and articles of the invention.
These and other objects of the invention as well as the advantages thereof can be had by reference to the following description and claims.